Sea water heat exchangers are commonly utilized in the oil and gas processing industry and in refineries where fresh water supplies may be limited. Design details of shell and tube type heat exchangers are described in Perry's Chemical Engineers' Handbook; 7th ed., McGraw-Hill. Reference is also made to the publications of the Tubular Exchanger Manufacturers Association (TEMA).
In chemical plant and refinery locations where sea water is plentiful and cheap, it is economically desirable to use sea water as the cooling medium in coolers for gases and liquids. However, because of its corrosivity, sea water has been used only as a coolant in coolers made from expensive corrosion-resistant alloys.
The alloy tube sheet protective cover duplicates the configuration and number and placement of the tube receiving holes in the carbon steel tube sheet. The alloy and carbon steel tube sheets are mechanically sealed at their periphery by means described below.
It is common practice to weld the extended end portion of the tube to the outside of the alloy tube sheet for sealing purposes. Welding is a time-consuming and costly manufacturing process for tube sheets with hundreds of tubes. Highly skilled and motivated welders are required to produce a quality product. Low quality welded joints can result in sea water leaks and the hidden corrosion of the carbon steel base plate. This problem is increased with passage of time when corrosive sea water coolant at high temperature is in contact with the carbon steel. Further, it is an expensive and time-consuming process to remove a tube with a welded end sealing joint from the alloy tube sheet. By eliminating welding, manufacturing and maintenance costs of such coolers would be reduced.
It is also known in the construction of shell and tube heat exchangers to insert the tubes into the holes in the tube carbon steel sheet and radially expand each of the tubes to secure it in place in a groove formed in the interior surface of the hole. There must be good mechanical bond strength and water tightness in the resulting joint between the tube sheet and each tube.
A method and apparatus for expanding a tube into a groove in the wall of a hole in a tube sheet is described in U.S. Pat. No. 4,142,581. However, this disclosure is not directed to the use of a sea water coolant and no sea water-resistant alloy tube sheet covering is present to protect the carbon steel tube sheet. There is also no corrosion-resistant alloy metal joint between the tubes and the tube sheet for sealing purposes and for corrosion protection of a carbon steel tube sheet.
The subject invention, produces a mechanically strong joint having chemical corrosion resistance to sea water. This joint permits the use of comparatively low cost method for protecting the carbon steel parts for the cooler, e.g., the shell and tube sheets.
Existing welding practices can now be replaced by the subject invention. In such case, there will be a savings in weld material, working time and speed up in the heat exchanger repair cycle. Also, the removal of tubes from the tube sheet will be easier in the absence of a welded seal.